Development of a Specialized Test Rig for Advanced Durability Diagnostics in PEM Water Electrolysis

EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476251 A1819 Page 1/7 A1819 Development of a Specialized Test Rig for Advanced Durability Diagnostics in PEM Water Electrolysis Dennys Erdtmann* (1), Maximilian Möckl (1), Franziska Wilfinger (1,2), Matthias Rzepka (1) (1) ZAE Bayern, Electrochemical Energy Storage, Garching/Germany; (2) Technical University Munich, Chair for Technical Electrochemistry, Garching/Germany; *Contact corresponding authors: www.EFCF.com/ContactRequest Abstract To enable the deployment of proton exchange membrane water electrolysis (PEMWE) at gigawatt scale for power-to-X hydrogen production, a deeper understanding of cell component degradation mechanisms is essential. In particular, this involves the possible release of active material from iridium-based oxygen evolution reaction (OER) catalysts, as well as fluoride from ionomer materials in membrane electrode assembly (MEA) setups. However, detecting dissolved iridium ions in the anode water cycle is challenging in commercially available test rigs due to galvanic replacement with less noble metallic components, such as stainless steel piping. As part of the H2Giga IRIDIOS project, we present a custom test rig designed for evaluating 16-cell stacks at up to 250 A, 30 bar, and 90 °C that is currently under construction. To prevent the redeposition of dissolution products, the anode side of the system is entirely metal-free, aside from two titanium electrodes used in water conductivity sensors as an essential part of the diagnostics. The in-house design enables dual online conductivity measurements, before and after the anode, along with the integration of a variety of advanced diagnostic tools for tracing fluoride and OER catalyst dissolution products. EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476251 A1819 Page 2/7 Introduction Proton exchange membrane water electrolysis (PEMWE) is considered a key technology for power-to-X hydrogen production, playing a vital role in the transition to a sustainable energy system [1]. Its advantages, including high efficiency, rapid responsiveness to fluctuating power inputs, high technological readiness level, and the ability to deliver hydrogen at elevated pressures, make it particularly well-suited for integration with renewable energy sources. However, the reliance on scarce and expensive noble metals such as platinum and iridium, used as catalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), remains a significant barrier to large-scale deployment. In particular, the limited availability of iridium threatens to become a bottleneck in the realization of gigawatt scale PEM hydrogen production [2]. Addressing this challenge requires the development of OER catalysts with reduced iridium loading and extended operational lifetimes while maintaining high performance. Degradation of stack components, both under operating conditions and during electrochemical testing, further constrains the economic viability of PEM electrolyzers [3, 4]. To develop resistant materials with improved lifetimes and gain insights into optimal operating routines, it is necessary to better understand the degradation mechanisms limiting long-term cell performance. As part of the H2Giga IRIDIOS project, we present an in-house design for a test rig optimized for testing stacks and single cells with regard to degradation analysis and lifetime optimization. The system supports testing of stacks with up to 16 cells at a maximum current of 250 A, differential pressures of 30 bar, and operating temperatures reaching 90 °C. Section 1 provides a brief overview of the main critical membrane electrode assembly (MEA) components and the associated degradation mechanisms that will be the focus of our future work. Section 2 outlines the measurement techniques that are supported by the test rig, as well as the relevant device specifications. 1. MEA Degradation Mechanisms Almost all MEA components (and other PEMWE cell components) are subject to degradation, including sealing gaskets, PTLs, catalysts, and bipolar plates [4]. However, our research primarily focuses on the ionomer membrane and the iridium-based OER catalyst. Chemical Membrane Degradation PEM electrolyzers use a perfluorinated sulfonic-acid (PFSA)-based ionomer membrane, typically Nafion, as electrolyte and to separate the product gases. Below a cell potential of 0.682 V vs. SHE, hydrogen peroxide radicals can be produced, which cause chemical degradation of the membrane [4], leading to membrane thinning and pinhole formation [3]. While thinner membranes improve efficiency by reducing ionic resistance, they are also more susceptible to degradation. This results in issues such as increased gas crossover and elevated cell overpotential. Ionic impurities in the water feed significantly accelerate membrane degradation [5]. Metallic cations such as Fe2+, Cu2+, and TiO2+ lower the proton conductivity of PFSA-based membranes due to their affinity for the SO3group of the polymer [6] and catalyze the production of hydrogen peroxide and subsequent fluoride emission, especially in the case of Fe2+ [7]. EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476251 A1819 Page 3/7 Loss of Active OER Catalyst Area Iridium is one of the most corrosion-resistant metals available. However, at high cell potentials during the OER, multiple dissolution pathways of the catalyst layer are triggered [8]. Loss of anode catalyst material can occur through four main pathways: dissolution into the anode water cycle, displacement into the membrane ionomer, redeposition at the cathode, and dissolution into the cathode water cycle. Milosevic et al. [9] performed accelerated stress tests (ASTs) of MEAs and subsequent post-mortem analysis and detected about 93% of lost iridium in the membrane and at the cathode, while only about 6% dissolved into the anode water cycle. Besides catalyst mass loss through dissolution, additional degradation phenomena include particle growth and morphological changes of the active catalyst layer [4]. Low iridium catalyst loading, high potential, and dynamic operation lead to accelerated loss of active catalyst area [10]. 2. Durability Diagnostics To detect and quantify the degradation phenomena outlined in Section 1, a number of measurement techniques are suitable [4]. The presented test rig is designed to combine as many diagnostics as feasible to gain optimal insight into the degradation of our prioritized MEA components. Specifically, the following methods are included. Standard Electrochemical Techniques The test station is equipped with standard electrochemical testing capabilities to measure polarization curves (max. 250 A, 48 V DC) and perform electrochemical impedance spectroscopy (EIS) at frequencies between 1 mHz and 100 kHz. Cyclic Voltammetry and Chronopotentiometry Cyclic voltammetry (CV) can provide valuable information about changes in active catalyst area and surface catalyst oxidation. While CV remains among the most commonly employed techniques in electrochemistry, it falls short when applied at stack level. This is because the applied voltage does not distribute equally over the stack, resulting in unequal individual cell voltages [11]. Chronopotentiometry (CP) mimics the CV signal by applying a constant current to the stack and transforming the voltage response of each individual cell to a pseudo-capacitance. This technique has recently been demonstrated by Wilfinger et al. [12] to be applicable to PEMWE stacks. A comparison of CV and CP data of a 5 cm² single cell at i = 5 mA/cm² is presented in Figure 1. EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476251 A1819 Page 4/7 Figure 1: Comparison of CV and CP measurements at i = 5 mA/cm² where imass is the current density normalized with respect to the iridium loading, v the CV sampling rate, and dE/dt the effective CP sampling rate [12]. Dual Conductivity Measurement (Anode) The anode water cycle is equipped with an ion exchanger that ensures water purity to be sufficient for normal operation. Immediately before the anode inlet and after the anode outlet, two titanium electrodes measure water conductivity (measurement range 0.02 – 50000 µS/cm). An increase in water conductivity is linked to the concentration of anode catalyst dissolution products. In order to avoid the redeposition of iridium or iridium oxide ions through galvanic replacement on less noble materials such as stainless steel piping [13, 14], the entire anode water cycle is constructed out of PTFE and PP, except for the titanium electrodes. In case of recirculation bypassing the ion exchanger, the metal-free design avoids membrane poisoning by cations originating from steel components [5, 6]. Conductivity Measurement (Cathode) Chemical degradation of the membrane causes the release of fluoride and sulphate ions [4]. These ions primarily leave the cell via the cathode water outlet, where OER catalyst dissolution products are not expected in significant amounts [9]. Marocco et al. [15] demonstrated that conductivity measurements are a reliable metric to measure fluoride concentration in DI-water. The test station is therefore equipped with a third conductivity sensor in the cathode water outlet, enabling online monitoring of fluoride concentrations. Gas Crossover (Hydrogen in Oxygen) While membrane thinning has a measurable effect on the cell overpotential and polarization curves, it is shown that this is not the case for pinhole formation [16], though a perforated membrane causes an increase in gas crossover rate. An accurate measurement of hydrogen in oxygen concentration in the oxygen product gas outlet (in addition to the safety H2 sensor monitoring the test rig vent) is therefore used as an online diagnostic for membrane perforation. Current Interrupt EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476251 A1819 Page 5/7 Current interrupt (CI) techniques provide a cost-efficient alternative to EIS and Tafel analysis and are also suitable for cells with very low impedance values, such as in large-scale industrial systems with increased active catalyst area. CI techniques use the initial cell voltage response after an abrupt drop in electric current to infer the ohmic resistance RΩ. With a more complex equivalent circuit model, Krenz et al. [17] demonstrated that a modified CI technique can also be used to fully characterize PEMWE cells, inferring charge transfer resistance Rct and double layer capacity Cdl in addition to RΩ. To the best of our knowledge, this technique has not yet been demonstrated at stack level. Accordingly, we aim to evaluate its applicability using EIS analysis as a benchmark. A prerequisite for the adequate extraction of information from CI data, however, is a sufficient time resolution between 5-10 ms. This requirement is not met by our currently used test station, which can provide a sampling rate of only 100 ms. The new test station design, therefore, includes measurement capabilities with sufficient time resolution. ICP-MS To support the in-situ detection of catalyst dissolution products via conductivity measurement, anode and cathode water samples are collected at regular intervals and designated drain points in the cathode and anode water during operation, to be analyzed by inductively coupled plasma mass spectroscopy (ICP-MS). 2. Conclusion and Outlook We presented a custom test rig design optimized for MEA degradation diagnostics on PEMWE stacks containing up to 16 cells. Common degradation mechanisms of the ionomer membrane and the OER catalyst material were summarized, as well as diagnostic techniques discussed that are supported by the test rig. Besides standard electrochemical techniques, this includes conductivity measurements in both the anode and cathode water, CV and CP, a hydrogen concentration measurement in the oxygen product gas, as well as automated online water sampling for ICP-MS analysis. In addition, cell voltage measurements have a sufficient sampling rate to support the testing of current interrupt techniques for PEMWE stacks. References [1] Buttler, A.; Spliethoff, H. Current Status of Water Electrolysis for Energy Storage, Grid Balancing and Sector Coupling via Power-to-Gas and Power-to-Liquids: A Review. Renew. Sustain. Energy Rev. 2018, 82, 2440–2454. https://doi.org/10.1016/j.rser.2017.09.003 [2] Minke, C.; Suermann, M.; Bensmann, B.; Hanke-Rauschenbach, R. Is Iridium Demand a Potential Bottleneck in the Realization of Large-Scale PEM Water Electrolysis? Int. J. Hydrogen Energy 2021, 46 (46), 23581–23590. https://doi.org/10.1016/j.ijhydene.2021.04.174 [3] Feng, Q.; Yuan, X.-Z.; Liu, G.; Wei, B.; Zhang, Z.; Li, H.; Wang, H. A Review of Proton Exchange Membrane Water Electrolysis on Degradation Mechanisms and Mitigation Strategies. J. Power Sources 2017, 366, 33–55. https://doi.org/10.1016/j.jpowsour.2017.09.006 EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476251 A1819 Page 6/7 [4] Wallnöfer-Ogris, E.; Grimmer, I.; Ranz, M.; Höglinger, M.; Kartusch, S.; Rauh, J.; Macherhammer, M.-G.; Grabner, B.; Trattner, A. A Review on Understanding and Identifying Degradation Mechanisms in PEM Water Electrolysis Cells: Insights for Stack Application, Development, and Research. Int. J. Hydrogen Energy 2024, 65, 381–397. https://doi.org/10.1016/j.ijhydene.2024.04.017 [5] Becker, H.; Murawski, J.; Shinde, D. V.; Stephens, I. E. L.; Hinds, G.; Smith, G. Impact of Impurities on Water Electrolysis: A Review. Sustainable Energy Fuels 2023, 7 (7), 1565–1603. https://doi.org/10.1039/D2SE01517J [6] Hongsirikarn, K.; Goodwin, J. G.; Greenway, S.; Creager, S. Effect of Cations (Na⁺, Ca²⁺, Fe³⁺) on the Conductivity of a Nafion Membrane. J. Power Sources 2010, 195 (21), 7213–7220. https://doi.org/10.1016/j.jpowsour.2010.05.005 [7] Frensch, S. H.; Serre, G.; Fouda-Onana, F.; Jensen, H. C.; Christensen, M. L.; Araya, S. S.; Kær, S. K. Impact of Iron and Hydrogen Peroxide on Membrane Degradation for Polymer Electrolyte Membrane Water Electrolysis: Computational and Experimental Investigation on Fluoride Emission. J. Power Sources 2019, 420, 54–62. https://doi.org/10.1016/j.jpowsour.2019.02.076 [8] Kasian, O.; Grote, J.-P.; Geiger, S.; Cherevko, S.; Mayrhofer, K. J. J. The Common Intermediates of Oxygen Evolution and Dissolution Reactions during Water Electrolysis on Iridium. Angew. Chem., Int. Ed. 2018, 57 (9), 2488–2491. https://doi.org/10.1002/anie.201709652 [9] Milosevic, M.; Böhm, T.; Körner, A.; Bierling, M.; Winkelmann, L.; Ehelebe, K.; Hutzler, A.; Suermann, M.; Thiele, S.; Cherevko, S. In Search of Lost Iridium: Quantification of Anode Catalyst Layer Dissolution in Proton Exchange Membrane Water Electrolyzers. ACS Energy Lett. 2023, 8 (6), 2682–2688. https://doi.org/10.1021/acsenergylett.3c00193 [10] Alia, S. M.; Stariha, S.; Borup, R. L. Electrolyzer Durability at Low Catalyst Loading and with Dynamic Operation. J. Electrochem. Soc. 2019, 166 (15), F1164. https://doi.org/10.1149/2.0231915jes [11] Génevé, T.; Turpin, C.; Régnier, J.; Rallières, O.; Verdu, O.; Rakotondrainibe, A.; Lombard, K. Voltammetric Methods for Hydrogen Crossover Diagnosis in a PEMFC Stack. Fuel Cells 2017, 17 (2), 210–216. https://doi.org/10.1002/fuce.201600073 [12] Wilfinger, F.; Möckl, M.; Schramm, C.; Ernst, M. F.; Kornherr, M.; Gasteiger, H. A. Chronopotentiometric Methodology to Characterize the Electrochemically Active Surface Area in PEM Water Electrolysis Cells and Stacks. ECS Meet. Abstr. 2024, MA2024-02 (45), 3109. https://doi.org/10.1149/MA2024-02453109mtgabs [13] Knöppel, J.; Möckl, M.; Escalera-López, D.; Stojanovski, K.; Bierling, M.; Böhm, T.; Thiele, S.; Rzepka, M.; Cherevko, S. On the Limitations in Assessing Stability of Oxygen Evolution Catalysts Using Aqueous Model Electrochemical Cells. Nat. Commun. 2021, 12 (1), 2231. https://doi.org/10.1038/s41467-021-22296-9 [14] Babic, U.; Tarik, M.; Schmidt, T. J.; Gubler, L. Understanding the Effects of Material Properties and Operating Conditions on Component Aging in Polymer Electrolyte EFCF 2025: Low-Temp. Fuel Cells, Electrolysers & H2 Processing 1 – 4 July 2025, Lucerne Switzerland https://doi.org/10.5281/zenodo.17476251 A1819 Page 7/7 Water Electrolyzers. J. Power Sources 2020, 451, 227778. https://doi.org/10.1016/j.jpowsour.2020.227778 [15] Marocco, P.; Sundseth, K.; Aarhaug, T.; Lanzini, A.; Santarelli, M.; Oyarce Barnett, A.; Thomassen, M. Online Measurements of Fluoride Ions in Proton Exchange Membrane Water Electrolysis through Ion Chromatography. J. Power Sources 2021, 483, 229179. https://doi.org/10.1016/j.jpowsour.2020.229179 [16] Liu, C.; Wrubel, J.; Padgett, E.; Bender, G. The Impacts of Membrane Pinholes on PEM Water Electrolysis. J. Power Sources 2023, 581, 233507. https://doi.org/10.1016/j.jpowsour.2023.233507 [17] Krenz, T.; Gottschalk, T.; Helmers, L.; Trinke, P.; Bensmann, B.; HankeRauschenbach, R. Current Interrupt Technique to Fully Characterize PEMWE Cells. J. Electrochem. Soc. 2024, 171 (3), 034509. https://doi.org/10.1149/1945-7111/ad3057 Keywords: EFCF2025, H2, LowTemp. Fuel Cells & Electrolysers, Durability Testing, Measurement Techniques, Test Station Development, MEA Degradation Remark: This work is licensed under Creative Commons Attribution 4.0 International